In vehicle bodies such as the van type having a substantially vertical rear access opening, there is by choice of vehicle design provided either a sideways type swinging tailgate that swings about a generally vertical axis and as a result requires little effort to open and close or a lift type tailgate that swings upward about a horizontal axis to open and as a result requires significant lifting effort. For the convenience of the people using a vehicle having a lift type tailgate, it is desired that a power lift system be provided to relieve a person of the required lifting effort and particularly where the tailgate is a heavy singular gate or door that closes the entire rear access opening. However, there is very limited space in the vehicle body for a power lift system with the capacity to handle the heavy lifting effort required of such a heavy lift type tailgate. Moreover, it is desirable that the tailgate be capable of being opened and closed manually independent of special conditioning of the power lift system and with minimum effort both as a matter of convenience and in the event the operation of the power lift system is not available for some reason such as a malfunction in the actuator mechanism or loss of power.
Previous power lift tailgate systems that do appear to work satisfactory in various respects are typically complicated in structure with many components and require considerable space such as those employing a sector gear and linkage system with connected counterbalancing devices to counterbalance the tailgate to reduce the lift load. Furthermore, they typically require a control system co-operating with certain of the actuating components to switch between a power mode and a manual mode that will allow manual opening and closing free of the power lift mechanism. Moreover, they are typically insensitive to the tailgate encountering an obstacle during powered movement.